1. Field of the Invention
This invention relates to a lighting element, and in particular to a wide-area lighting element in which the light is provided by a plurality of relatively small discrete light sources such as light emitting diodes (LEDs). The lighting element of the invention has relatively low power consumption, can be made in a number of different colors, is flexible so that it can be constructed in the form of a tube or attached to a curved surface, and yet provides a uniform light output similar to that provided by a fluorescent light.
The flexibility and light diffusion effect of the lighting element of the present invention both result from the inclusion of the microprism sheet, which may be made of a flexible resin material such as an acrylic or polyvinyl chloride, and which may either be provided with a diffusion coating or may otherwise be treated to provide a desired diffusion effect.
2. Description of Related Art
Light emitting diodes have a number of advantages over conventional lighting elements, including relatively low power consumption, the ability to emit light of different colors, and durability. However, because of the small size of LEDs, they cannot be used to provide wide area lighting of the type conventionally provided by fluorescent lights.
The present invention combines the conventional LEDs into a new type of lighting element, in which light from the individual LEDs is diffused through a microprism sheet to provide a lighting effect similar to that provided by a fluorescent light, and yet that is flexible and can therefore be formed into a wide variety of configurations, including tube-shaped structures capable of emulating a fluorescent light tube, without the relatively high power consumption of a conventional fluorescent light tube or the need for an electronic ballast. By using a microprism sheet to diffuse light emitted by the LEDs, the light is combined in a more uniform manner than is possible with conventional diffusers, which do not have the selective light bending properties of a microprism sheet.
The use of microprism sheets having light diffusing properties for purposes such as glare reduction overlays, rear or front projection screens, or light-diffusion screens of the type interposed between the back of an liquid crystal diode (LCD) screen and a light source, is of course well-known. Examples of prior microprism arrangements involving light diffusion are disclosed, for example, in U.S. Pat. No. 3,718,078 (Plummer), U.S. Pat. No 3,902,787 (Sherlock), U.S. Pat. No. 4,309,073 (Nishimura et al.), and U.S. Pat. No. 5,837,346 (Langille et al.). In general, however, in contrast to the present invention, the microprism sheet arrangements disclosed in these references use the diffusion properties to smooth out irregularities or hot spots with respect to light or images that are spread out over a relatively large area.
Additional examples of microprism sheets which may be provided with light diffusing properties are disclosed in copending U.S. patent application Ser. No. 09/481,942, filed Jan. 13, 2000, which discloses a number of microprism sheet treatment arrangements, in the context of privacy screens, interlacing arrangements and light separating arrangements, but not specifically for use in lighting elements.
On the other hand, a lighting arrangement involving use of microprism sheets in connection with "point sources" such as LEDs is disclosed in U.S. Pat. No. 5,835,661 (Tai et al.). The system disclosed in this patent seeks "the conversion of light from a point-like light source to a linear or planar light beam having a sufficiently uniform distribution of light" by employing a light pipe combined with microprism structures which are used to divert light out of the light pipe over an extended surface. The lighting arrangement disclosed in U.S. Pat. No. 5,835,661 is said to be useable in displays, road signs, medical research equipment, instrument meters or jewelry, light pictures or art work, or for surgical or dental lighting, but nevertheless is disadvantageous because of its relative complexity and because the lighting elements disclosed in the patent is are limited to rigid rather than flexible structures. The present invention is intended to be suitable for use not only in the applications listed in U.S. Pat. No. 5,835,661, but also in a variety of additional lighting applications requiring more flexible, low power, wide area lighting.